Using Metamod:Source on Listen Servers
Since the September 8, 2010 Patch it is necessary to add -insecure to the launch options to load third party plugins like Metamod.
The launch option must be removed again to join other (secure) servers. So for convenience it might be best to create suitable desktop short cuts.
Old Metamod versions
Note: The instructions below are only intended for users of older Metamod:Source versions (1.4.2 or lower), which do not support the newer loading mechanism. If you are using Metamod:Source 1.4.3+ or higher and you are using a metamod.vdf file, these instructions do not apply to you.
To run your Source listen server with Metamod:Source, you need to install Metamod:Source with the automated installer or simply download the latest version of the launcher from SVN. If you decide to use the binary from SVN, copy the file into your server's game directory (the directory where you can find the game's hl2.exe).
Using the Launcher
Before you can use the launcher, make sure Steam is already started. Once you know it is, you only need to start "hl2launch.exe" in your game directory. You can also specify (typical) Counter-Strike:Source parameters like "-console" or simply create a link to it on your desktop.
When you use this tool, always make sure Steam is already running. If that's the case and you get an error message when starting your game with the launcher, try to run it once from the Steam Games menu and start it again with the tool.